This application relates to a method for scavenging aldehydes such as formaldehyde, irrespective of the source from which the aldehyde is derived, utilizing bisulfite salts.
Aldehydes, especially formaldehyde, are widely used in resin compositions. Certain of these resin compositions are extensively used in the manufacture of construction materials such as decking, paneling, shelving, cabinets, etc.; in home furnishings such as furniture, carpeting, drapery and upholstery fabrics and in foam insulation. Typically, these resin compositions contain a substantial molar excess of formaldehyde. Some of this excess formaldehyde is released upon curing of the resin during the manufacture of the product e.g., particle board. However, the problem is that formaldehyde continues to be released from these products after the manufacturing process is completed. There are several sources of this released formaldehyde, e.g. unreacted excess formaldehyde, hydrolysis and products formed from the reaction of formaldehyde and urea, as well as decomposition of the resin from age, humidity, temperature, weathering, etc. Formaldehyde is very volatile, has a very unpleasant odor which irritates the eyes and nasal passages and may give rise to other health problems. Although to date, no evidence links formaldehyde as being a toxic, carcinogenic or mutagenic substance, it is very important for both health and aesthetic reasons not only to limit the concentration of aldehydes in the environment during the production of the products utilizing aldehyde based resins but also to minimize the amounts of aldehyde released from these products over the useful life of these products. Several methods have been explored for reducing aldehyde release from the above-mentioned products, by the incorporation of additives into the adhesive resins, but it has not been possible to eliminate the aldehyde liberation therefrom over an extended period of time. Other methods have been explored for reducing the concentration of airborne aldehyde especially formaldehyde emitted from these products, or any other sources by the use of coatings, plastic films (polyethylene) placed over the board products, as well as the use of mechanical devices containing odor absorbers, air refreshers, etc. These methods have only reduced the rate of the aldehyde liberation, but not the amount liberated.
Furthermore, the rate at which the aldehyde is liberated depends upon the temperature, the relative humidity of the environment, the loading factor, i.e. the type of products, the surface area of the products and the resin formulations used to prepare the products, etc.
Therefore, there is a need for effective methods not only to reduce the amount of aldehyde released during the manufacture and subsequent use of the resin containing products but also for a method to remove airborne aldehydes from the environment irrespective of their source.
A discussion of the problems and earlier methods for reducing the odor emitted from formaldehyde based resins and the products derived therefrom is presented in U.S. Pat. No. 4,264,760. That patent describes a method for deodorizing formaldehyde based resins by adding to the resin, sulfur-containing compounds primarily the oxyacid salts of sulfur in which the sulfur valence ranges from +5 to -2 inclusive. The sulfur concentration ranges from 0.3 to 30% by weight of the total resin. The formaldehyde to sulfur molar ratio can be between 1 to 10 and 10 to 7 but it is preferable to keep the range within molar matching of the reagents. To be effective, in reducing the amount of formaldehyde release, the resin plus the sulfur compound additive mixture must be cured either by exposure to low pH or to heat. The patent cites several examples of various formaldehyde based resins in which the amount of formaldehyde released is reduced after 24 hours by 15-40% on treatment with the sulfur based additives. Specifically a 2-4% by weight 1:1 molar mixture of sodium sulfite:sodium bisulfite additive reduces the amount of formaldehyde released after three weeks from urea-formaldehyde insulation foam by 27-31%. While sodium bisulfite is suggested within the broad classification of oxyacid salts of sulfur, no where is the use of sodium bisulfite alone disclosed to be an effective scavenger of formaldehyde.
Accordingly, an object of the present invention is to provide a method for reducing the amount of aldehydes liberated during the production of and subsequent use of aldehyde releasing products.
A further object is to provide a method for scavenging from the environment aldehydes irrespective of their source.